Liquid phospholipid-containing compositions for the preparation of pharmaceuticals

ABSTRACT

Current krill oil extracts are liquid at room temperature and include only about 45-55% phospholipids. As the purity of phospholipids increases, the extracts become more viscous, making them difficult to handle and process. The invention mixes these pure materials with viscosity-reducing agents to make them amenable to processes such as encapsulation. Thus the invention retains the useful liquid characteristics of known krill extracts while providing much higher concentrations of phospholipids.

This application claims the benefit of United Kingdom patent application 1402450.9 filed Feb. 12 2014, the complete contents of which are incorporated herein by reference for all purposes.

TECHNICAL FIELD

The invention relates to liquid compositions which can be used for preparing pharmaceutically acceptable capsules for oral administration of highly purified krill phospholipids.

BACKGROUND OF THE INVENTION

There is accumulating evidence of the benefits of dietary intake of the long chain omega-3 fatty acids found in fish, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). These fatty acids have been shown to decrease the risk of coronary heart disease and ischemic heart disease, and the products Lovaza®, Omacor®, and Vascepa® are approved for human use.

The molecular form of omega-3 fatty acids (e.g. triglycerides or ethyl esters) may be important to their biological effect and their distribution in the body. Krill oil contains a high proportion of omega-3 fatty acids incorporated in phospholipids and it has been demonstrated that krill oil had stronger effects than fish oil on specific parameters related to metabolic syndromes [1]. Moreover, krill is abundant, can be harvested easily, and is very low in the food chain which results in a relative lack of pollution-derived contaminants.

Current krill oil products (e.g. Superba™ and Onemia™) are prepared as oral capsules, which is relatively straightforward in view of the oil's physicochemical properties. But as the purity of the products increase, giving higher proportions of krill phospholipids, the inventors have found that these physicochemical properties change, and highly-purified material is a waxy solid which is not amenable to direct encapsulation e.g. when at least 85% of the oil is krill phospholipids.

It is an object of the invention to provide ways of encapsulating these purified krill phospholipids.

DISCLOSURE OF THE INVENTION

The invention combines purified krill phospholipids with a viscosity-reducing agent, thereby giving them flow properties which are compatible with preparing oral capsules. Viscosity is maintained within a useful range while providing a higher concentration of phospholipids than seen in current krill oil extracts. Thus the invention retains the useful liquid characteristics of known krill extracts while providing much higher phospholipid concentrations.

The invention therefore provides a pharmaceutically acceptable liquid composition comprising purified krill phospholipids and a viscosity-reducing agent.

The invention also provides a pharmaceutically acceptable oral capsule including encapsulated liquid contents, wherein the liquid contents comprise purified krill phospholipids and a viscosity-reducing agent.

The invention also provides a process for preparing a pharmaceutically acceptable liquid composition, comprising a step of mixing purified krill phospholipids with a viscosity-reducing agent.

The invention also provides a process for preparing a pharmaceutically acceptable oral capsule, comprising steps of (a) mixing purified krill phospholipids with a viscosity-reducing agent; and (b) encapsulating the mixture from step (a) into a pharmaceutically acceptable oral capsule.

The invention also provides a process for preparing a pharmaceutically acceptable oral capsule, comprising a step of encapsulating into a pharmaceutically acceptable oral capsule a mixture of purified krill phospholipids and a viscosity-reducing agent.

The invention also provides a pharmaceutically acceptable liquid composition having a viscosity of less than 3000 mPa·s when measured at a temperature within the range 25-70° C., wherein the composition comprises (i) at least 80% by weight of a phospholipid-containing krill extract which has a viscosity of at least 3000 mPa·s when measured at a temperature where the liquid composition has a viscosity of less than 3000 mPa·s and (ii) no more than 20% by weight of viscosity-reducing agent.

The invention also provides a process for preparing a pharmaceutically acceptable liquid composition having a viscosity of less than 3000 mPa·s when measured at a temperature within the range 25-70° C., comprising a step of mixing (i) a phospholipid-containing krill extract which has a viscosity of at least 3000 mPa·s when measured at a temperature where the liquid composition has a viscosity of less than 3000 mPa·s with (ii) a viscosity-reducing agent, wherein components (i) and (ii) are mixed at a ratio of at least 80% by weight (i) and no more than 20% by weight (ii).

The invention also provides a process for preparing an oral capsule comprising steps of: (a) mixing (i) a phospholipid-containing krill extract which has a viscosity of at least 3000 mPa·s at 25° C. with (ii) a volatile solvent, to give a liquid composition having a viscosity of less than 3000 mPa·s at 25° C.; (b) inserting the liquid composition into a capsule; and (c) storing the capsule under conditions such that at least a portion of the volatile solvent escapes from the capsule such that viscosity of the capsule's contents increases to at least 3000 mPa·s at 25° C.

The invention also provides an oral capsule whose contents include purified krill phospholipids, wherein the contents have a viscosity of at least 3000 mPa·s at 25° C.

The invention also provides a liquid composition comprising purified krill phospholipids and glycerol. The inclusion of glycerol means that the composition is particularly suitable for filling into gelatin capsules which include glycerol as a shell component, because it has been seen that glycerol tends to migrate from the shell into the capsule contents. Thus the invention also provides an oral capsule for human use (particularly one which includes glycerol as an ingredient e.g. as a plasticiser) including an encapsulated liquid composition, wherein the liquid composition comprises purified krill phospholipids and glycerol.

Liquid Compositions

The invention provides pharmaceutically acceptable liquid compositions which comprise purified krill phospholipids and a viscosity-reducing agent (and, optionally, one or more further components).

These liquid compositions are useful as the encapsulated liquid contents of oral capsules for pharmaceutical use.

The viscosity-reducing agent reduces the intrinsic viscosity of the purified phospholipids so that the mixture can be handled easily, for instance when preparing oral capsules. Ideally, the mixture has a viscosity (dynamic viscosity) within the range 10-3000 mPa·s at a temperature within the range 25-70° C. Thus, within at least a portion of this temperature range, the mixture will exhibit a viscosity within this range, but it is not necessary that the mixture has this viscosity across the complete temperature range. For instance, it might have a viscosity of >3000 mPa·s at 25° C. but a viscosity within the range of 10-3000 mPa·s at a higher temperature e.g. at 40° C. or above. Viscosity can be measured using a shear rate of 100 s⁻¹ over a period of 20 minutes.

Within the range of 10-3000 mPa·s, it is preferred that viscosity should not exceed 1000 mPa·s, so a viscosity within the range 50-1000 or 100-1000 mPa·s is a preferred option.

In addition to this viscosity property, the mixture should remain homogeneous when subjected to shear stress at shear rates up to 100 s⁻¹. Thus the mixture remains liquid under these conditions, and does not undergo precipitation, crystallisation, or phase separation. The mixture therefore retains useful handling properties under shear conditions which could be experienced during the preparation of oral capsules.

To achieve these viscosity reductions, various viscosity-reducing agents can be mixed with the purified phospholipids, including hydrophilic additives, lipophilic additives, amphiphilic additives, and mixtures thereof. Suitable hydrophilic additives include, but are not limited to, lower alcohols (C1-C6 alcohols e.g. ethanol, 2-propanol, 1-propanol), benzyl alcohol, glycerol, and glycols (e.g. propylene glycol, or a polyethylene glycol such as PEG-300, PEG-400, or PEG-600). Suitable lipophilic additives include, but are not limited to, vegetable oils (e.g. castor oil, sesame oil), triglycerides (e.g. medium-chain triglycerides or MCTs, glyceryl trioctanoate, glyceryl trioleate, etc.). Suitable amphiphilic additives include, but are not limited to, surfactants such as polysorbates (e.g. polysorbate 80 or 20). Generally a viscosity-reducing agent will include two or three different components (see below).

In all cases the components of the viscosity-reducing agent should be pharmaceutically acceptable. Where an organic solvent is included, such as a lower alcohol, it is preferred to use only those solvents which are regarded as safe in humans. Pharmaceutically acceptable organic solvents are classified in Q3C ‘class 3’ (i.e. acetic acid, heptane, acetone, isobutyl acetate, anisole, isopropyl acetate, 1-butanol, methyl acetate, 2-butanol, 3-methyl-1-butanol, butyl acetate, methylethyl ketone, tert-butylmethyl ether, methylisobutyl ketone, cumene, 2-methyl-1-propanol, dimethyl sulfoxide, pentane, ethanol, 1-pentanol, ethyl acetate, 1-propanol, ethyl ether, 2-propanol, ethyl formate, propyl acetate, and formic acid). Thus compositions of the invention are preferably free from organic solvent components which are not in this list e.g. they should be free from chloroform and hexane (and optionally also free from dichloromethane). Thus, where a composition of the invention includes an organic solvent (whether as a residual component in the phospholipids or as a component of the viscosity-reducing agent), this is preferably a ‘class 3’ solvent, and it is even more preferred that a composition should include only 1 or 2 organic solvents in total e.g. only ethanol.

The amounts of viscosity-reducing agent which is used to achieve the desired reduction in viscosity can readily be determined by following the guidance given herein. To maximise the phospholipid concentration within the liquid, however, the amount of viscosity-reducing agent should be kept to a low level. Ideally, the proportion of viscosity-reducing agent should be no more than 20% by weight of the liquid composition e.g. within the range of 5-15%. Thus, for instance, the liquid material can include from 5-20% by weight viscosity-reducing agent and from 80-95% by weight krill oil extract, wherein the krill oil extract includes 85% by weight or more of krill phospholipids.

To achieve the desired viscosity with such low levels of viscosity-reducing agent, it is preferred to use a mixture of two components as the viscosity-reducing agent. Typically, a lower alcohol will be included within the range of about 2-10% by weight of the liquid composition (e.g. 5-10%) as part of the viscosity-reducing agent, and also a second additive (e.g. MCTs or a PEG) within the range of 5-10% by weight of the liquid composition. The remainder of the liquid composition can be krill oil with a high content of purified phospholipids. As mentioned below, where the second additive is a PEG, the alcohol can be used at lower concentrations, thereby permitting higher phospholipid concentrations to be achieved.

Some embodiments of the invention use a viscosity-reducing agent which comprises a hydrophilic additive (such as a lower alcohol) and a lipophilic additive. For example, the viscosity-reducing agent can be a mixture of ethanol and MCTs. MCTs are a mixture of triglycerides of saturated fatty acids, mainly of caprylic acid and capric acid, and can include a minimum of 95% by weight of C₈ and C₁₀ saturated fatty acids. They are usually obtained from coconut oil or palm kernel oil.

Such mixtures give useful viscosity, but they tend to require quite high levels of alcohols (e.g. above 5%) and of triglycerides, and thus lower concentrations of phospholipids. Thus it may be preferred to use a viscosity-reducing agent which comprises a lower alcohol and a further hydrophilic additive (e.g. a glycol) as lower amounts of these agents can achieve the same viscosity reduction. For instance, a lower alcohol such as ethanol can usefully be combined with a polyethylene glycol (PEG) or propylene glycol. PEGs having a molecular weight of less than 1000 can be used, and both PEG400 and PEG300 (i.e. PEGs with an average molecular weight of 400 and 300, respectively) have provided useful viscosity reductions even with only 2.5% or 5% by weight ethanol and 12.5% by weight PEG400.

One useful viscosity-reducing agent is based on a mixture of PEG, MCTs, and glycerol. Mixtures of PEG and glycerol, and of MCTs and glycerol, are also useful. A mixture of ethanol with one or more of PEG, MCTs, and glycerol can also be used. PEG600 is preferred in these mixtures.

By keeping the amount of viscosity-reducing agent low (e.g. less than 20% or 15% by weight, or even 10% or less), the amount of phospholipids can be correspondingly high. With ≧80% by weight of a krill oil which includes ≧85% by weight krill phospholipid, the liquid can include ≧680 mg/mL of krill phospholipids. With lower amounts of viscosity-reducing agent and higher purity of phospholipids within a krill extract, the concentration of krill phospholipids can reach 900 mg/mL or more. Thus a liquid composition of the invention can include krill phospholipids at a concentration within the range 680-900 mg/mL e.g. ≧700 mg/mL, ≧750 mg/mL, ≧800 mg/mL, or ≧850 mg/mL, or higher. For instance, the concentration can be between 720-850 mg/mL. In contrast, the concentration of krill phospholipids in Superba™ capsules is less than 500 mg/mL.

These high concentrations can be achieved by using phospholipids of high purity i.e. where the phospholipids make up a high proportion of the krill material which is combined with a viscosity-reducing agent to form the liquid composition of the invention. Krill phospholipids of high purity can be prepared in various ways from krill oil e.g. see references 2-5. Purities of 85% by weight or more (weight of krill phospholipids out of total weight of lipids) can be achieved using these methods (e.g. 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more) and the invention uses krill phospholipids having such purity.

Compared to known krill oil extracts such as Superba™ and Onemia™, which include only about 45-55% phospholipids, these purified phospholipids are highly viscous (waxy solids, even) and so require the addition of a viscosity-reducing agent to make them amenable to processes such as encapsulation. The viscosity-reducing agent can reduce the viscosity into a useful range (e.g. 10-3000 mPa·s) without simultaneously reducing the concentration of the phospholipids to the relatively low levels seen in Superba™ and Onemia™. Thus the invention retains the useful liquid characteristics of known krill extracts while providing much higher levels of phospholipids.

Ideally, the viscosity-reducing agent is not naturally present within krill oil, such that its presence immediately signifies that the composition goes beyond mere purification of phospholipids from krill. Even if the viscosity-reducing agent is similar to components present within krill oil, simple analysis can confirm that the composition is not merely a purified krill material e.g. by detecting the relative proportions of components. A mixture of purified krill phospholipids and a lipophilic viscosity-reducing agent (e.g. MCTs) can easily be distinguished from less pure krill oil extracts (e.g. Superba™ or Onemia™) by analysis of its lipid composition. For instance, the fatty acid profile of MCTs differs from the fatty acid profile of the non-phospholipid fraction of krill oils.

The liquid compositions can be prepared by simple mixing of the purified krill phospholipids with and the viscosity-reducing agent. In some embodiments this mixing process can form a homogeneous suspension, but the invention ideally uses a clear solution i.e. the phospholipids are dissolved in the viscosity-reducing agent to give a clear solution having the desired properties. Where the viscosity-reducing agent includes more than one component, the mixing may take place in various stages e.g. mixing the phospholipids with a first component of the viscosity-reducing agent, and then mixing this intermediate mixture with a second component of the viscosity-reducing agent (for example, mix the phospholipids with MCTs, and then combine this mixture with ethanol) to give the final desired liquid composition.

Oral Capsules

The invention permits the preparation of pharmaceutically acceptable oral capsules from highly purified krill phospholipids. These capsules take the form of hollow shells, within which liquid compositions (liquid at least at the time of filling into the shells) containing krill phospholipids are encapsulated. They are intended to be swallowed whole by a patient, after which the shell breaks down and releases the capsule's contents into the gastrointestinal tract.

The invention can be used with both hard capsules and soft capsules. Hard capsules are made of two shells: the capsule body and a cap. The cap fits snugly over the open end of the capsule body, thereby forming the enclosed shell. To ensure reliable closing of the filled capsules, shells with locking grooves or indentations are often used. The grooves or indentations fit into each other for tight closing and they prevent accidental separation of the assembled capsule. The joint between the two capsule parts can be sealed (e.g. with a gelatin or polymer band, or via thermal bonding). Hard capsules are typically made from gelatin, but gelatin-free hard capsules are also known e.g. made from hypromellose (hydroxypropyl methylcellulose; HPMC), pullalan, PVA copolymer, or starch. Mixtures of materials can also be used e.g. gelatin and polyethylene glycol, HPMC and carrageenan, HPMC and pectin, etc. In addition to these materials, hard capsules can include colourings, water, plasticizers, sugars, etc.

Where the invention uses a hard capsule, it should have a size and shape which are amenable to human swallowing. Hard capsule shells are manufactured in various standard sizes. For human use, capsules ranging in size from 000 (the largest) to 5 (the smallest) are commercially available, but size 00 is typically seen as the largest form acceptable for comfortable oral use. Details of standard capsule sizes are below [6], although details and tolerances may vary by manufacturer:

Size 000 00 0 1 2 3 4 5 Volume (mL) 1.37 0.95 0.68 0.50 0.37 0.30 0.21 0.13 Length (mm) 26.14 23.3 21.7 19.4 18.0 15.9 14.3 11.1 Outer 9.91 8.53 7.65 6.94 6.35 5.82 5.31 4.91 diameter (mm)

Where the invention uses a hard capsule, it is typically of size 00, 0, 1, 2, 3 or 4. Larger sizes can, of course, provide larger amounts of krill phospholipids, but for any size of capsule the invention permits higher doses to be delivered than has previously been possible because it uses krill phospholipids of higher purity.

The invention can also use soft capsules. These are one-piece hermetically-sealed soft shells, typically prepared by a rotary-die process in which two continuous gelatin ribbons are brought together between twin rotating dies, where material is injected between the ribbons as they form the shell within the dies. The two sheets are sealed by pressure and heat and then separated from the ribbons. Drop formation processes are also used, which can provide seamless capsules. Soft capsules generally have thicker shells than hard capsules. They are typically made from gelatin, but gelatin-free hard capsules are also known e.g. made from starches, carrageenans, or combinations thereof. In addition to these materials, soft capsules usually include a plasticizer (e.g. sorbitol, xylose, maltitol, glycerin), and they can also include colourings, water, and sugars. Soft capsules can be preferred for volatile liquid contents or for materials which are susceptible to deterioration in the presence of air. Thus soft capsules are preferred for the present invention. Soft gelatin capsules which include glycerol as a plasticiser can be used, and in this situation it is advantageous that the liquid contents should also include glycerol.

Where the invention uses a soft capsule, it should have a size and shape which are amenable to human swallowing. Soft capsules come in various shapes (including spherical/round, oval/elliptical, and oblong) and sizes, including various standard sizes including 1 round, 2 round, 3 round, 4 round, 5 round, 6 round, 7 round, 2 oval, 3 oval, 4 oval, 5 oval, 6 oval, 7 oval, 10 oval, 20 oval, 3 oblong, 4 oblong, 5 oblong, 6 oblong, 8 oblong, 9.5 oblong, 5 tube, 6 tube, and 8 tube (e.g. see chapter 13 of ref. 7). The number in these size designations represents the maximum internal volume of the capsule in minims (where 16.23 minims=1 mL) e.g. a 12 oval capsule can encapsulate up to 0.74 mL. The materials used to make the capsules should be pharmacopoeial-grade e.g. USP or PhEur. Pharmacopoeial-grade gelatins and starches are routinely available.

Capsule Filling Process

The normal process for preparing a hard oral capsule involves inserting the desired contents into the body, and then fitting the cap. To prevent leakage of liquid contents the joint between body and cap can then be sealed. The normal process for preparing a soft capsule is discussed above. For both operations the reduction in viscosity provided by the invention gives material which can be handled easily by existing machinery for filling capsules. Unfortunately, the addition of a viscosity-reducing agent tends to increase hygroscopicity, thereby leading to higher levels of lysophospholipids which emerge during storage (although still at very low levels overall, e.g. ≦1%).

One way to address this issue is to use a volatile solvent as part of the viscosity-reducing agent. This permits viscosity to be reduced (as discussed above) while the capsules are being filled, as desired. Once the capsule has been sealed, however, the inventors have observed that volatile solvents can escape from the capsules during storage (particularly under drying conditions), which means that viscosity of the contents increases again, which leads to less water entry and thus a longer shelf-life.

The invention therefore provides a process comprising steps of: (a) mixing (i) a phospholipid-containing krill extract which has a viscosity of at least 3000 mPa·s at 25° C. with (ii) a volatile solvent, to give a liquid composition having a viscosity of less than 3000 mPa·s at 25° C.; (b) inserting this liquid composition into a capsule; and (c) storing the capsule under conditions such that at least a portion of the volatile solvent escapes from the capsule such that viscosity of the capsule's contents increases to at least 3000 mPa·s at 25° C.

This process can be used to provide an advantageous oral capsule whose contents include purified krill phospholipids, wherein the contents have a viscosity of at least 3000 mPa·s at 25° C.

Step (a) of the process is the same as discussed above, except that the viscosity-reducing agent must comprise a volatile solvent. Suitable solvents include lower alcohols as discussed above, such as ethanol. The volatile solvent will typically not be used on its own e.g. a mixture of ethanol with PEG, MCTs, or glycerol can be used. The viscosity-reducing agent containing the volatile solvent reduces the viscosity of the phospholipid material.

This material is then inserted into a capsule, such as a soft capsule, as discussed above. Soft gelatin capsules are typical, as these can readily permit escape of volatile solvents.

Sealed capsules are then stored to permit the volatile solvent to escape from the capsule's contents. This can occur during the formal process of drying which follows capsule filling prior to packaging e.g. in a drying room. Drying for about 3 days is generally enough to permit solvent to escape, and thus for viscosity to increase. Typically, at least 20% (by weight) of the volatile solvent escapes from the capsules, and often even more e.g. ≧25%, ≧30%, ≧33%, or more.

Krill Phospholipids

Compositions of the invention include krill phospholipids. As noted above, krill phospholipids with purities of 85% by weight or more can be prepared. Preferred purification methods can reduce levels of impurities such as trimethylamine N-oxide (TMAO), astaxanthins, lysophospholipids, and free fatty acids, to give highly pure krill phospholipid compositions and increase the efficiency of their delivery by oral capsules.

The krill phospholipids can be from any species of krill, including Antarctic krill (Euphausia superba), Pacific krill (Euphausia pacifica) and Northern krill (Meganyctiphanes norvegica). In addition to E. superba, other species are known to live in the Antarctic, one in genus Thysanoessa (T macrura) and six in genus Euphausia. These include ice krill (Euphausia crystallorophias), E. frigida, E. longirostris, E. triacantha and E. vallentini. The preferred krill species is E. superba.

The krill phospholipids used with the invention preferably comprise a mixture of phospholipid compounds of formula (I) as described in detail below:

wherein:

-   -   R₁ and R₂ are each independently selected from a fatty acid         moiety of formula —COC_(n)H_(m), a fatty acid moiety of formula         —CH₂C_(n)H_(m), and —H;     -   R₁ and R₂ include omega-3 fatty acid moieties, such that at         least 30% by weight of the phospholipid compounds is composed of         omega-3 fatty acid moieties;     -   at least 90% by weight of total omega-3 fatty acid moieties are         at position R₂;     -   R₁ and R₂ are not both —H in a phospholipid compound, and R₁ or         R₂ is —H in less than 15% by weight of the compounds of formula         (I), and ideally in less than 3% by weight of the compounds of         formula (I);     -   R₃ is selected from —H, a choline moiety, an ethanolamine         moiety, a N-acetylethanolamine moiety, an inositol moiety, and a         serine moiety; and     -   R₃ is a choline moiety in at least 85% by number of the         compounds of formula (I).

Typically, and as explained in more detail below, the krill phospholipid compositions also have one or more of the following properties:

-   -   (a) at least 85% by weight of the composition consists of         phospholipid compounds of formula (I);     -   (b) the weight ratio of C16:0/C14:0 fatty acid moieties in the         mixture is between 10:1 and 18:1 and/or the weight ratio of         C18:4 n-3/C18:3 n-3 fatty acid moieties is between 1:1 and 3:2;     -   (c) the composition includes less than 300 μg astaxanthins per         gram of phospholipid;     -   (d) the composition comprises less than 0.01% by weight         trimethylamine N-oxide     -   (e) the composition comprises less than 0.01% by weight         homarine;     -   (f) the composition includes less than 5% by weight water;     -   (g) the composition has less than about 0.03% by weight PUFA         polymers     -   (h) the phospholipid mixture includes both phospholipids where         R₁ is a fatty acid moiety of formula —COC_(n)H_(m) and         phospholipids where R₁ is a fatty acid moiety of formula         —CH₂C_(n)H_(m);     -   (i) the phospholipid mixture includes both phospholipids where         R₁ is an omega-3 fatty acid moiety and phospholipids where R₂ is         an omega-3 fatty acid moiety;     -   (j) the composition includes less than 5% by weight         sphingomyelin; and/or     -   (k) the composition is free from chloroform and hexane.         R₁ and R₂

R₁ and R₂ are each independently selected from the group consisting of a fatty acid moiety of formula —COC_(n)H_(m), a fatty acid moiety of formula —CH₂C_(n)H_(m), and —H. R₁ or R₂ is —H in only a small fraction of the compounds of formula (I) i.e. less than 3% by weight of the phospholipid compounds are lysophospholipids (see below). Thus most R₁ and R₂ are —COC_(n)H_(m) or —CH₂C_(n)H_(m). Where R₁ or R₂ has formula —COC_(n)H_(m) the fatty acid moiety has an ester linkage, but where R₁ or R₂ has formula —CH₂C_(n)H_(m) the fatty acid moiety has an ether linkage. In these formulae C_(n)H_(m) refers to the aliphatic chain which is seen in a naturally-occurring fatty acid (e.g. as seen in krill). For any value of n, m=2n+1 when the fatty acid moiety's aliphatic chain is saturated, but m is reduced by 2 for each unsaturated bond (double bond) in the aliphatic chain i.e. m=2n−1 if one unsaturated bond is present, m=2n−3 if two double bonds are present, m=2n−5 if three double bonds are present, etc. Thus, in general, n is an integer in the range of 4-24 and m=2(n−p)+1, where p is the number of double bonds in the fatty acid moiety. As disclosed in reference 8, the value of n for krill is generally within the range of 11 to 21, and krill phospholipids can include fatty acid moieties with up to six double bonds.

Typically, where a fatty acid moiety at position R₁ or R₂ is of formula —CH₂C_(n)H_(m), the fatty acid moiety is either saturated or monounsaturated. Thus, where R₁ or R₂ is of formula —CH₂C_(n)H_(m), the relationship between n and m is m=2n+1 at that position. In a single molecule, however, it is possible to have a fatty acid moiety of formula —COC_(n)H_(m) at one of R₁ and R₂ (i.e. ester-linked) and a fatty acid moiety of formula —CH₂C_(n)H_(m) at the other of R₁ and R₂ (i.e. ether-linked). Furthermore, usually 90% (molar) or more of the ether-linked fatty acid moieties will generally be C16 and/or C18 (i.e. where n=15 or 17), unsaturated (e.g. C16:0) or monounsaturated (e.g. C18:1), and ether-linked omega-3 fatty acid moieties are generally not present. Overall, within the mixture, it is preferred that no more than 10% by number of the fatty acid moieties are of formula —CH₂C_(n)H_(m) (i.e. 10% or fewer of fatty acid moieties are ether-linked, and more than 90% are ester-linked). It is preferred, though, that the phospholipid mixture should include ether-linked fatty acid moieties i.e. they should not be undetectable. Ether-linked fatty acid moieties are readily detected and quantified by NMR (e.g. see reference 8).

In general, R₁ and R₂ are not both of formula —CH₂C_(n)H_(m) in any single phospholipid molecule. Furthermore, fewer than 5% by number (e.g. fewer than 1% by number, or even zero) of the phospholipid molecules in the mixture have R₂ of formula —CH₂C_(n)H_(m). In other words, ether-linked fatty acid moieties within the mixture may be seen at R₁, but not at R₂. Thus, in some embodiments: R₁ is selected from a fatty acid moiety of formula —COC_(n)H_(m), a fatty acid moiety of formula —CH₂C_(n)H_(m), and —H; and R₂ is selected from a fatty acid moiety of formula —COC_(n)H_(m), and —H.

In some embodiments: R₁ is selected from a fatty acid moiety of formula —COC_(n)H_(m), a fatty acid moiety of formula —CH₂C_(n)H_(m) where m=2n±1, and —H; and R₂ is selected from a fatty acid moiety of formula —COC_(n)H_(m), and —H. Thus, within the mixture: R₁ is an ester-linked fatty acid, an ether-linked saturated or monounsaturated fatty acid, or hydrogen; and R₂ is either an ester-linked fatty acid moiety or hydrogen; provided that R₁ and R₂ are not both hydrogen in a single molecule.

The term “fatty acid” as used herein refers to a carboxylic acid with an unbranched aliphatic chain, which may be saturated or unsaturated. These have the general formula C_(n)H_(m)—COOH Long chain polyunsaturated fatty acids (LC-PUFAs) are in general fatty acids that have a n value of 19 or more. Polyunsaturated refers to unsaturation at two or more bonds. The term “fatty alcohol” refers to an alcohol with an unbranched aliphatic chain, which may be saturated or unsaturated, and they have the general formula C_(n)H_(m)—CH₂OH. The term “fatty acid moiety” as used herein refers to the aliphatic chain C_(n)H_(m) from such fatty acids and fatty alcohols, and the nature of the moiety can be defined by referring to the corresponding fatty acid and/or fatty alcohol. Thus, for a fatty acid moiety of formula —COC_(n)H_(m) or —CH₂C_(n)H_(m) the corresponding fatty acid is C_(n)H_(m)—COOH and the corresponding fatty alcohol has formula C_(n)H_(m)—CH₂OH. By way of example the fatty acid DHA (C₂₁H₃₁COOH) corresponds to a fatty acid moiety of formula —COC₂₁H₃₁ or —CH₂C₂₁H₃₁, and EPA (C₁₉H₂₉COOH) corresponds to a fatty acid moiety of formula —COC₁₉H₂₉ or —CH₂C₁₉H₂₉.

R₁ and R₂ can thus be fatty acid moieties that contain saturated or unsaturated aliphatic chains, but at least 30% by weight of the phospholipid mixture is composed of omega-3 fatty acid moieties at the R₁ and R₂ positions (i.e. omega-3 fatty acid moieties provide at least 30 g for every 100 g of phospholipid compounds in the mixture). Omega-3 fatty acids are polyunsaturated fatty acids whose final double bond is positioned between the third and fourth carbon atoms from the methyl end of the hydrocarbon chain. Non-limiting examples of omega-3 fatty acids include 5,8,11,14,17-eicosapentaenoic acid (EPA), 4,7,10,13,16,19-docosahexanoic acid (DHA) and 7,10,13,16,19-docosapentanoic acid (DPA). At least 90% by weight of total omega-3 fatty acid moieties in a phospholipid mixture are at position R₂ within formula (I). At least 50% by weight of total omega-3 fatty acid moieties in a phospholipid mixture are EPA and/or DHA (i.e. weight of DHA and EPA/total weight of omega-3 fatty acid moieties in the phospholipids of formula I).

The weight contribution of total omega-3 fatty acid moieties at the R₁ and R₂ positions can be determined by extracting total phospholipids from the mixture e.g. using the method of reference 9. This is followed by hydrolysis of the lipids to release fatty acids. The released fatty acids are converted to fatty acid esters e.g. fatty acid methyl esters and these esters are analysed e.g. by gas chromatography, HPLC, etc. For instance, the American Oil Chemists' Society has published AOCS Official Method Ce 1b-89 for determining the fatty acid composition of marine oils and marine oil esters by capillary column gas-liquid chromatography. Similarly, reference 8 discloses quantitative analysis of krill oil using HPLC methods based on references 10 and 11 (using evaporative light scattering detection or charged aerosol detection). These established methods provide the amount of specific fatty acids present in a sample, from which the amount of omega-3 fatty acids present in the sample (i.e. in positions R₁ and R₂ of the phospholipid mixture) can be calculated. In general, references to the content of lipid or phospholipid compositions on a weight/weight basis as referred to herein should be taken as having been determined on the basis of these methods (extraction as in reference 9, followed by processing and analysis by chromatography).

Preferably the phospholipid mixture comprises between 30-40% w/w omega-3 fatty acid moieties.

In some embodiments, the phospholipid mixture comprises both EPA and DHA fatty acid moieties, in which case the EPA and DHA moieties are preferably present in a molar ratio of EPA:DHA of from about 1:1 to about 3:1 (e.g. about 1.5:1 to 2:1 or about 1.8:1 to 2.2:1).

Phospholipid mixtures used with the invention differ from reference 12, where R₁ and/or R₂ is/are —OH 20-50% of the phospholipids, rather than being a fatty acid moiety, and where transesterification is used to provide a mixture having as much as 35% lysophospholipids.

Lysophospholipids are formed by hydrolysis of fatty acids from phospholipids, resulting in phospholipids with a single fatty acid moiety. Thus one of R₁ or R₂ is —H in these lysophospholipid compounds. The invention seeks to avoid high levels of lysophospholipids, and the processes of the invention result in low concentrations of lysophospholipids, namely ≦3% w/w and preferably less than 2%, less than 1%, or even less than 0.5% (weight of lysophospholipid/weight of total phospholipids of formula I). The amount of lysophospholipid may be determined by the HPLC-based analytical methods referred to above, and also by NMR or HP-TLC.

In one embodiment the mixture has a lysophospholipid content of between 1.1-3% w/w, but in other embodiments the mixture has a lysophospholipid content of less than 0.9% w/w. In some embodiments, however, the mixture can have a lysophospholipid content much higher than this, but less than 15% w/w e.g. <10%, or <5%. In general, however, a lysophospholipid content of less than 3% w/w, and typically <2% or <1%. Lysophospholipids are surfactants and they cause the formation of micelles and tubular systems in the presence of water, which leads to a change in rheological properties and, in particular, an increase in viscosity, so their presence is not desirable.

R₁ and R₂ are not both —H in a phospholipid compound. Furthermore, within the composition, it is preferred that molecules of formula (I) where R₁ and R₂ are both hydrogen are undetectable.

R₃

R₃ is H or is selected from a choline, ethanolamine, N-acetylethanolamine, inositol and serine. Choline moieties predominate at R₃, and the mixture of phospholipid compounds comprises more than 80% choline moieties at position R₃ on a molar % basis (mol of choline moieties/total mol phospholipid compounds of formula I), and preferably more than 85% e.g. at least 86, 87, 88, 89, or 90% choline moieties at position R₃ on a molar % basis. The mixture of phospholipid compounds can comprise at least 1% (e.g. about 3-15%, 5-12%, 7-10% or 8-9%) ethanolamine and/or N-acetylethanolamine moieties at position R₃ on a molar % basis, and preferably a mixture includes at R₃ choline and either or both of ethanolamine and/or N-acetylethanolamine. The mixture of phospholipid compounds can comprise <1% of inositol moieties at position R₃ on a molar % basis. These amounts can be determined for example by using NMR. The methods referred to above can also be used to determine the amounts of these components on a w/w basis (in which the amount of each may be expressed in g/100 g oil).

Within the mixture, for molecules where R₃ is a choline moiety, it is preferred that around 5-15% by number of these molecules have an ether-linkage at position R₁. Thus, where R₃ is choline, 5-15% of these molecules have R₁ of formula —CH₂C_(n)H_(m), where m=2n±1.

Within the mixture, for molecules where R₃ is an ethanolamine or N-acetylethanolamine moiety, it is preferred that around 35-45% by number of these molecules have an ether-linkage at position R₁. Thus, where R₃ is ethanolamine or N-acetylethanolamine, 35-45% of these molecules have R₁ of formula —CH₂C_(n)H_(m), where m=2n±1.

Phosphorous-containing groups in phospholipids used with the invention may exist in a number of protonated and deprotonated forms depending on the pH of the surrounding environment, for example the pH of the solvent system in which they are dissolved. Therefore, although a particular form may be illustrated in the formula shown above with a negatively-charged O⁻ group, this is intended to be merely representative and does not limit the invention to a specific protonated or deprotonated form.

Phospholipid Concentration

In some embodiments at least 85% by weight of a krill-derived composition consists of phospholipid compounds of formula (I) e.g. >90%, >95%, >96%, >97%, >98%, or even >99%. The low level of impurities means that such compositions are particularly suitable for pharmaceutical use.

These highly pure compositions can be obtained via the use of acetone precipitation, but it is preferred that the compositions are substantially free from residual acetone. Acetone is classified by ICH guideline Q3C as a class 3 solvent i.e. as having low toxic potential. Recommended intake of such solvents is 50 mg per day or less, and so a composition of the invention ideally has an acetone content of less than about 0.5% by weight e.g. less than 0.1%, or less than 0.01%. Acetone removal is very efficient and can achieve levels as low as 20 mg per kg of purified krill phospholipid (i.e. 0.002% by weight or 20 ppm). Alternatively defined, the phospholipids used with the invention can be essentially free from acetone.

Although preferred compositions are those in which, as discussed above, at least 85% by weight of the composition consists of phospholipid compounds of formula (I), in some embodiments this figure may be reduced, and the invention also contemplates compositions in which at least 75% or 80% by weight of the composition consists of phospholipid compounds of formula (I).

Fatty Acid Signature

A phospholipid mixture used with the invention can have: (i) a weight ratio of C16:0/C14:0 fatty acid moieties of between 10:1 and 18:1 e.g. between 12:1 and 16:1; and/or (ii) a weight ratio of C18:4 n-3/C18:3 n-3 fatty acid moieties of between 1:1 and 3:2. In these embodiments the phospholipid mixture does include (i) both C16:0 and C14:0 fatty acid moieties and/or (ii) both C18:4 n-3 and C18:3 n-3 fatty acid moieties.

Astaxanthins

Contrary to the preference in reference 2, where krill phospholipids include 3 g/kg astaxanthins, phospholipids used with the invention ideally include very low levels of astaxanthins (i.e. free astaxanthin and esters thereof) because, despite their advantageous antioxidant properties, the inventors see these compounds as pharmacological impurities which have a biological effect. The phospholipids used with the invention can have a concentration of astaxanthins which is less than 300 μg per gram of phospholipid (i.e. less than 0.03% by weight), and preferably less than 0.01% by weight. Phospholipids used with can even have less than 0.002% by weight astaxanthins (i.e. <20 mg astaxanthins per kg phospholipids) or less than 0.001%. Astaxanthin content can be measured by HPLC e.g. using UV detection.

Levels of astaxanthins are expressed herein as diol equivalents i.e. as free astaxanthin, without including the weight of any esterification (e.g. to fatty acids).

TMAO

In some embodiments phospholipids used with the invention comprise less than 0.01% by weight TMAO e.g. 0.005%. Ideally, TMAO is undetectable. TMAO is removed primarily by washing step (b). TMAO levels can also be expressed relative to the phospholipid compounds. As such the TMAO content can be expressed as a molar ratio such that compositions of the invention have a molar excess of phospholipids to TMAO of at least 1,000.

In addition to having low or no TMAO, compositions of the invention can also have less than 0.005% by weight trimethylamine (TMA) e.g. undetectable TMA.

TMA and TMAO can contribute to an unpleasant smell in a composition, and they can also lead to undesirably high viscosity.

Homarine

Homarine (N-methylpicolinic acid) is a morphogenetically active quaternary ammonium base which occurs in tissues of various marine animals, including krill. In some embodiments phospholipids used with the invention comprise less than 0.01% by weight homarine e.g. 0.005%. Ideally, homarine is undetectable.

Water Content

Phospholipids used with the invention can have a water content of less than about 5% w/w, and preferably less than about 4, 3, 2, or 1% w/w. Ideally, a composition of the invention is as dry as possible, so a water content of <2% w/w, such as <1% or even <0.5% is desirable. The phospholipids are quite hygroscopic in pure form, though, so they should be stored appropriately and can be re-dried after storage prior to being used for preparing compositions as disclosed herein.

PUFA Polymers

In some embodiments phospholipids used with the invention have a low concentration of polymers of polyunsaturated fatty acids. Preferably they have less than about 0.03, 0.02, or 0.01% w/w PUFA polymers. Polymer content is measured e.g. by NMR or gel permeation chromatography.

Sphingomyelins

Sphingomyelins are sphingophospholipids found in animal cell membranes. They are based on sphingosine, which is an 18-carbon amino alcohol with an unsaturated hydrocarbon chain, and they usually consist of phosphocholine (PC) and ceramide, or a phosphoethanolamine (PE) head group. Reference 3 discloses a krill polar lipid extract obtained using hexane and acetone, including 8% sphingomyelins. Phospholipids used with the invention can include less than 5% by weight sphingomyelin, or less than 4%, and generally include much less than this (or even zero). Thus phospholipids used with the invention may include less than 1% by wt sphingomyelin e.g. <0.1%, <0.01%, or <0.001%.

Residual Organic Solvents

As mentioned above, it is preferred in compositions of the invention to use only pharmaceutically acceptable solvent components which are regarded as safe in humans. Thus phospholipid compositions used with the invention are preferably free from organic solvent components which are not in this list e.g. they should be free from chloroform and hexane. If a phospholipid composition includes a residual organic solvent, this is preferably a ‘class 3’ solvent, and it is even more preferred that a composition with residual organic solvent should include residues of only 2 or 3 organic solvents in total e.g. residue only of ethanol and acetone.

Omega-6 Fatty Acid Moieties

Omega-6 fatty acids can be inflammatory, so they are ideally kept at low levels in compositions of the invention. Thus in some embodiments of the invention the total amount of omega-6 fatty acids (in particular those contributed by the phospholipid mixture) is less than 2% by weight, and ideally less than 1.5% or even less than 1%.

Starting Krill Materials for Preparing Phospholipids

For purifying phospholipids for use with the invention, rather than starting directly with krill organisms it is preferred to start with krill which have been processed e.g. as disclosed in any of references 13, 14, or 15. Dry or wet krill pastes can be made, but the preferred starting material is wet krill paste. As already known in the art (e.g. see example 4 of reference 13), such a paste can be obtained e.g. by heat treatment of krill organisms in water, separation of solid and aqueous materials by filtration to provide a krill milk, coagulation by heating, separation by filtration, and then pressing to remove water. A process of the invention can thus include an initial step of obtaining wet krill paste from live krill. Heating krill organisms soon after capture can inactivate their endogenous lipases, which can help to ensure that starting material used with the invention has a low intrinsic level of lysophospholipids, thereby reducing the need to remove these impurities during the process of the invention.

Preferred Phospholipid Mixtures

With reference to the features mentioned above, a preferred mixture of phospholipid compounds of formula (I) has properties (a), (c), (d), (h), and (k) as noted above. This composition preferably also has property (f) and/or properties (e) and (j). Thus a composition with all of properties (a), (c), (d), (e), (f), (h), (j), and (k) is particularly preferred.

With reference to property (h), fatty acid moieties of formula —CH₂C_(n)C_(m) are either saturated or mono-unsaturated, and not polyunsaturated, such that m=2n±1. The value of n is from 11-21.

Usually, the compounds of formula (I) in such compositions will include (1) both C16:0 and C14:0 fatty acid moieties and/or (2) both C18:4 n-3 and C18:3 n-3 fatty acid moieties. Such compositions should also have characteristic (b) as noted above. Preferably the phospholipids include C16:0, C14:0, C18:4 n-3 and C18:3 n-3 fatty acid moieties.

When the mixture has property (f), the amount of water is ideally less than 2% by weight.

Further useful properties of these preferred mixtures are:

-   -   (l) the composition has less than 1% by weight free fatty acids;     -   (m) the composition has less than 0.005% by weight         trimethylamine; and/or     -   (n) the composition is free from canthaxanthin and flavonoid.

Thus one preferred composition has properties (a), (b) (c), (d), (e), (f), (h), (j), (k), (l), (m), and (n), wherein: with reference to property (h) fatty acid moieties of formula —CH₂C_(n)C_(m) are either saturated or mono-unsaturated, and not polyunsaturated; the compounds of formula (I) include C16:0, C14:0, C18:4 n-3 and C18:3 n-3 fatty acid moieties; and wherein the amount of water is optionally less than 2% by weight.

In these compositions the phospholipids of formula (I) can include EPA and DHA moieties in a molar ratio (EPA:DHA) of from 1.8:1 to 2.2:1.

Medical Uses of Compositions and Capsules of the Invention

The invention provides a composition comprising purified krill phospholipids and a viscosity-reducing agent for use in medicine. It also provides a capsule of the invention for use in medicine.

The invention also provides the combined use of purified krill phospholipids and a viscosity-reducing agent in the manufacture of a medicament. The medicament is ideally a capsule.

The invention also provides a method for treating a subject, comprising a step of administering to the subject a medicament comprising a purified krill phospholipids and a viscosity-reducing agent. The medicament is ideally a capsule of the invention.

Liquid compositions, medicaments, and capsules of the invention should be pharmaceutically acceptable for human beings.

Pharmaceutical compositions and medicaments of the invention are suitable for various medical uses, particularly in humans. For instance, they can be used to reduce serum triglycerides, reduce serum cholesterol, reduce or prevent plaque formation, reduce or prevent platelet aggregation, treat or prevent atherosclerosis, treat or prevent cardiovascular disease, treat or prevent inflammatory diseases, treat auto-immune diseases, treat coronary heart disease, treat depression, treat Alzheimer's disease, treat attention deficit disorder, treat sickle cell disease, or treat metabolic syndrome. Thus a subject who received a medicament of the invention may have one of these conditions, or be in need of one of these effects.

In some embodiments, krill phospholipids are administered in a daily dose of from about 0.1 to about 3 grams.

MODES FOR CARRYING OUT THE INVENTION Example 1: Krill Phospholipid Preparation

This example describes the extraction of oil from a wet material. A coagulum from krill comprising about 70% water, 15% lipids and about 15% other dry matter, mainly proteins, was obtained as described in reference 14. This material was subjected to an extraction procedure as follows. 3500 grams of pure ethanol was added to 1004 grams of the coagulum and stirred for 45 minutes. The mixture was then filtered through a filter paper applying vacuum on the receiving flask to obtain 3854 gram of filtrate. 1179 gram of the filtrate was subjected to evaporation on a rotary evaporator and the obtained dry matter was washed 4 times with a 60% solution of ethanol and finally the solvent was evaporated in a rotary evaporator. The obtained oil, 23.7 gram, was solid at room temperature and comprised 76.8% phospholipids. The content of EPA was 200 mg/gram and the content of DHA 87 mg/gram oil.

Example 2: Krill Phospholipid Preparation with Higher Purity

This example describes an alternative method for extraction of oil from the krill wet material, starting from a frozen paste from krill, which was subjected to an extraction procedure as described below. Unlike example 1, all steps were performed under a nitrogen atmosphere.

A frozen krill paste was subjected to an extraction procedure under a nitrogen atmosphere. The paste comprises about 65% water (assessed via dry matter), 17% lipids (about equal weights of phospholipids and neutral lipids), and about 18% other dry matter, mainly proteins.

100 kg of the frozen coagulum (−20° C.) was added to a vessel. Based on the water content of the coagulum, 350 kg of pure ethanol (99.8% w/w, room temp) was then added to the vessel, giving a final ethanol concentration in the liquid phase of about 84% w/w (˜350 kg ethanol in 415 kg liquid solvents).

The mixture was stirred in the vessel for 45 minutes, with gentle heating if required. Four final temperatures were studied in separate batches, namely a) 2° C., b) 10° C., c) 15° C. and d) 20° C. After stirring was complete, the mixtures were allowed to settle, and they each included a red-coloured liquid phase and a wet slurry containing shell fragments and other insoluble materials. To remove the liquid phase from the slurry the mixtures were decanted, and the liquid material was put through a coarse filter and then serial-filtered through a 75 μm and 5 μm cartridge filter to obtain a) 345 kg, b) 366 kg, c) 372 kg or d) 374 kg of filtrate, with residual material remaining in the filtration cake.

The filtrates were then subjected to a sequence of washes. Firstly, de-ionized water was added to give ˜60% w/w ethanol solutions (a: 137 kg water; b: 149 kg; c: 152 kg; d: 155 kg) and the mixtures were stirred for 10-15 minutes and left to settle for 12-24 hrs at room temperature (15-20° C.) in vessels having a valve at the base. The bottom phase was isolated by draining the bottom phase through the valve, to give between 5.4-9.0 kg of a lipid-rich fraction. The lipid-rich fraction was re-washed 2 to 5 times with 60% w/w ethanol at room temperature to give a final material which contained about 80% by weight phospholipids and 20% neutral lipids. In even the first wash, 85% of TMAO was removed, and the further washes led to material with undetectable TMAO (less than 1 mgN/100 g i.e. at least 20-fold lower than reported in Table X of reference 16).

This lipid-rich material was treated by cold acetone precipitation. Three parts w/w acetone were added and the lipid rich material was dissolved by gentle heating and slow stirring. The stirring was stopped and the mixture was cooled to 4° C. for precipitation. When the precipitation was complete, the upper solvent phase was removed. This cold precipitation procedure was performed three times in total, after first re-dissolving in fresh acetone each time.

The precipitate was then subjected to evaporation and freeze-drying to remove residual acetone and water. Batch c (i.e. extracted at 15° C., then washed 3×60% EtOH before cold acetone precipitation) provided 1.9 kg of solid material (an orange wax) consisting of 98% phospholipids/1.7% neutral lipids with a water content of 3%. Astaxanthins were present at <2 mg/kg. Amino acids, TMAO and homarine were all below the limit of quantification by standard analytical methods.

Looking at specific fatty acids, proportions were as follows, measured across several batches:

C14:0 C16:0 16/14 Ratio C18:3 n-3 C18:4 n-3 18:4/18:3 Ratio Wet paste  6-10% 15-17%  2-2.5 1.4-3.1% 3.5-7%  2-3  Final material 1.0-1.5% 15-17% 12-16 1.0-2.5% 1.0-2.5% 1-1.5

The purified phospholipids included both ether-linked and ester-linked fatty acids, but 10% or fewer were ether-linked. NMR showed ether-linked fatty acid moieties at position sn1 but not at sn2, and ether-linked fatty acids were either fully saturated or were monounsaturated. Where a phospholipid was a PC, about 10% of the molecules included ether-linked fatty acids; where a phospholipid was a PE (with or without N-acetylation), about 40% of the molecules included ether-linked fatty acids. PUFAs were seen only with ester linkages. 30-40% by weight of fatty acids in the purified phospholipids were omega-3, and these were distributed at the sn1 and sn2 positions (mainly at sn2). Most of the omega-3 fatty acids were EPA and/or DHA, with about 2× more EPA than DHA.

The Lyso-PC content (0.2-0.4 mol %) is very low in the purified phospholipids, when compared to the amount in the starting wet material (about 1.2-1.4 mol %). No molecules were detected where fatty acid chains had been lost at both the sn1 and sn2 positions. Lyso-PE (with or without N-acetylation) and lyso-PI also were not seen.

Thus the krill phospholipids obtained by this method have a high purity and a low level of specific contaminants. They are thus well-suited to pharmaceutical use, but their physical state (waxy solid, with a high viscosity even when warmed to 70° C.) is inconvenient for pharmaceutical preparation.

Example 3: Liquefaction of Purified Phospholipids

The material purified according to example 2 (or similar methods) is very viscous and sticky, which makes it unsuitable for filling into capsules. Thus purified krill phospholipids were thus combined with various hydrophilic and lipophilic additives as viscosity regulating agent:

Hydrophilic additives Lipophilic additives Ethanol Medium-chain triglycerides Glycerol Castor oil Propylene glycol Sesame oil PEG 300 Glyceryl Trioctanoate PEG 400

In early experiments, purified krill phospholipids (98% purity—see example 2) were mixed with MCTs and fully evaporated. The mixture was dissolved in excess ethanol and excess ethanol was removed by rotary evaporation. Results were as follows, where % s are expressed by weight:

Krill PLs (dry mass) (%) MCT (%) EtOH (%) Result Test 1 88.52 8.85 2.63 Fine viscosity Test 2 91.34 4.69 3.97 Slightly higher than Test 1 Test 3 89.26 8.92 1.8 Too viscous for easy handling Test 4 89.37 8.94 2.48 Too viscous for easy handling

Based on these results, 19 further compositions were designed and evaluated for viscosity using a variety of different viscosity-reducing agents. Viscosity was measured at both 25° C. and 40° C., using a shear rate of 100 s⁻¹ using an AG-G2 Rheometer with 40 mm plate/plate and 500 μm gap. Viscosity measurements were as follows, along with an observation whether the compositions remained homogeneous:

Sample KPL Viscosity-reducing Ethanol Viscosity Homog- # (wt %) agent (wt %) (wt %) Temperature (Pa · s) eneous 1 82.9 MCT 9.3 7.8 25° C. 3 No 82.9 9.3 7.8 40° C. 3 No 2 85.5 MCT 9.6 4.9 25° C. 12 No 85.5 9.6 4.9 40° C. 7 No 3 89.1 MCT 4.7 6.2 25° C. 7 No 89.1 4.7 6.2 40° C. 2 No 4 90.8 MCT 5.1 4.1 25° C. 52 No 90.8 5.1 4.1 40° C. 5 No 5 85.6 MCT 12.9 1.5 25° C. 31 No 85.6 12.9 1.5 40° C. 5 No 6 92.3 None 0.0 7.7 25° C. 4 Yes 92.3 0.0 7.7 40° C. 6 Yes 7 83.6 MCT 12.8 3.7 25° C. 7 No 83.6 12.8 3.7 40° C. 12 No 8 84.2 Castor oil 8.5 7.3 25° C. 3 No 84.2 8.5 7.3 40° C. 2 No 9 88.1 Castor oil 8.8 3.1 25° C. 8 No 88.1 8.8 3.1 40° C. 6 No 10 85.5 Glyceryl 8.6 6.0 25° C. 4 No 85.5 Trioctanoate 8.6 6.0 40° C. 5 No 11 83.1 Glyceryl 8.3 8.6 25° C. 1 No 83.1 Trioctanoate 8.3 8.6 40° C. 3 No 12 86.2 Sesame oil 8.8 5.0 25° C. 4 No 86.2 8.8 5.0 40° C. 11 No 13 83.5 Sesame oil 8.5 8.0 25° C. 3 No 83.5 8.5 8.0 40° C. 4 No 14 81.3 Glycerol 8.2 10.5 25° C. 2 Yes 81.3 8.2 10.5 40° C. 2 Yes 15 85.1 Glycerol 8.5 6.5 25° C. 10 Yes 85.1 8.5 6.5 40° C. 8 Yes 16 85.2 Propylene 8.7 6.1 25° C. 2 Yes 85.2 glycol 8.7 6.1 40° C. 2 Yes 17 89.0 Propylene 8.9 2.0 25° C. 7 Yes 89.0 glycol 8.9 2.0 40° C. 4 Yes 18 84.5 PEG 300 8.5 7.0 25° C. 2 Yes 84.5 8.5 7.0 40° C. 1 Yes 19 89.2 PEG 300 9.1 1.8 25° C. 12 Yes 89.2 9.1 1.8 40° C. 4 Yes

Further test compositions were prepared using ≧80% by weight of the purified phospholipids and a variety of viscosity-reducing agents using ethanol and one further component. The appearance and viscosity of these compositions was evaluated visually at room temperature. The following compositions have been prepared (% s are by weight):

Viscosity-reducing Krill PL agent EtOH Visual result Test 5 80 Sesame oil 15 5 Homogenous. Viscous but flows OK. Test 6 80 Soybean oil 15 5 Homogenous. Viscous but flows OK. Test 7 80 Propylene 15 5 Flows nicely, but a few lumps were glycol observed indicating inhomogeneity. Test 8 80 PEG 300 15 5 Homogenous, very good flow. Test 9 80 PEG 400 15 5 Homogenous, very good flow (even better than Test 8). Test 10 85 PEG 400 15 0 Homogenous but very viscous. Test 11 85 PEG 400 12.5 2.5 Homogenous. Flows OK. Test 12 90 PEG 400 7.5 2.5 Homogenous but extremely viscous. Test 13 87 PEG 400 10.5 2.5 Homogenous. Flows OK.

Further viscosity-reducing agents were tested as follows:

Krill Viscosity (Pa · s) PL EtOH PEG400 PEG600 MCT Glycerol 25° C. 30° C. Test 14 82.5 5 12.5 — — — 2987 1848 Test 15 82.5 5 — — 12.5 — 4229 3345 Test 16 80 7.5  7.5 — — 5 1595 — Test 17 80 7.5 —  7.5 — 5 737 — Test 18 82.5 5 — 12.5 — — 2271 1708

All five of these were clear and homogenous, although ‘Test 15’ was not as stable as the others.

In these test compositions, the concentration of phospholipids in the liquid materials comfortably exceeded 680 mg/mL, and generally fell within the range of about 720-850 mg/mL.

Example 4: Encapsulation Studies

Krill phospholipids of ˜98% purity (example 2) were formulated according to the ‘Test 9’ viscosity-reducing agent, whereas a krill extract with ˜80% phospholipids purity (example 1) was formulated like the ‘Test 11’ viscosity-reducing agent. The flow properties of these liquid materials were suitable for filling into oral capsules (viscosity at 30° C. was 1270 mPa·s for the 98% purity material, and 1870 mPa·s for the 80% purity material), so it was encapsulated into soft gelatin capsules which included both glycerol and sorbitol as plasticisers. Stability was assessed over a 12 week period, with stability parameters including the amount in the capsule contents of phosphatidylcholine, lysophosphatidylcholine, ethanol, water, glycerol, and sorbitol. Results at the start of the study and after 12 weeks at 40° C. were as follows:

80% purity 98% purity Parameter Time zero 12 weeks Time zero 12 weeks PC content 59.4%  58.7%  70.4%  70.4%  LPC content 0.42%  1.09%  0.25%  0.99%  EtOH content 1.3% 1.4% 3.7% 3.5% H₂O content 3.8% 4.2% 5.2% 5.3% Glycerol content 2.8% 6.5% 3.8% 7.8% Sorbitol content 0.3% 0.8% 0.4% 1.0%

Therefore the phospholipids were stable in the capsules, with very low levels of lyso-PC breakdown products being seen even after 12 weeks at 40° C. It was clear, however, that components from the capsule material (water, sorbitol, and particularly glycerol) were entering the contents. The liquid material which was used to fill the capsules contained no glycerol or sorbitol, and ≦1.2% water.

One way to inhibit migration of glycerol from the capsule into the contents is to include glycerol already within the liquid contents, as part of the viscosity-reducing agent.

Ethanol levels at time zero were 1.3% or 3.7%, whereas in the initial phospholipid mixture which was used to fill the capsules the level was 2.5% or 5%, respectively. Thus from 25-50% of the ethanol escaped from the capsules between filling and the beginning of the stability study i.e. during drying and storage. This loss of solvent is accompanied by an increase in viscosity of the contents.

It will be understood that the invention is described above by way of example only and modifications may be made while remaining within the scope and spirit of the invention.

REFERENCES

-   [1] Batetta et al. (2009) J Nutr 139:1495-1501. -   [2] WO2011/050474. -   [3] Watanabe et al. (1991) Nippon Suisan Gakkaishi 57:681-94. -   [4] WO2014/207571. -   [5] PCT/EP2015/050370. -   [6] Guidance for Industry—Size, Shape, and Other Physical Attributes     of Generic Tablets and Capsules—U.S. Department of Health and Human     Services, Food and Drug Administration, Center for Drug Evaluation     and Research (CDER), December 2013. -   [7] The Theory and Practice of Industrial Pharmacy. Lachman et al.     (3rd edition). -   [8] Winther et al. (2011) Lipids 46:25-36. -   [9] Bligh & Dyer (1959) Can. J. Biochem. Physiol 37:911-917. -   [10] Homan R et al. (1998) J Chromatogr B Biomed Sci Appl 708:21-26. -   [11] Moreau et al. (2006) Lipids 41:727-734. -   [12] US 2008/0058286. -   [13] WO2009/027692. -   [14] WO2008/117062. -   [15] WO2010/097701. -   [16] WO2013/102792. 

1. A pharmaceutically acceptable liquid composition comprising purified krill phospholipids and a viscosity-reducing agent, wherein the krill phospholipids have a concentration of at least 680 mg/mL.
 2. (canceled)
 3. An oral capsule for human use including an encapsulated liquid composition, wherein the liquid composition comprises purified krill phospholipids and a viscosity-reducing agent, wherein the krill phospholipids have a concentration of at least 680 mg/mL in the liquid composition.
 4. (canceled)
 5. The capsule of claim 3, wherein the oral capsule is a soft capsule for human oral use.
 6. (canceled)
 7. An oral capsule for human use including an encapsulated liquid composition, wherein (a) the capsule is made from a material which includes glycerol, and (b) the liquid composition comprises purified krill phospholipids and glycerol.
 8. A liquid composition having a viscosity of less than 3000 mPa·s when measured at a temperature within the range 25-70° C., wherein the composition comprises (i) at least 80% by weight of a phospholipid-containing krill extract which has a viscosity of at least 3000 mPa·s when measured at a temperature where the liquid composition has a viscosity of less than 3000 mPa·s and (ii) no more than 20% by weight of a viscosity-reducing agent.
 9. (canceled)
 10. The liquid composition of claim 8, wherein the liquid composition has a viscosity of less than 3000 mPa·s when measured at a temperature within the range 25-70° C.
 11. The liquid composition of claim 8, wherein the viscosity-reducing agent comprises: (i) a lower alcohol and a glycol; (ii) glycerol; or (iii) polyethylene glycol, medium-chain triglycerides, and glycerol.
 12. The liquid composition of claim 8, wherein the liquid composition comprises (a) less than 20% by weight of viscosity-reducing agent and (b) 80-95% by weight krill oil, wherein the krill oil includes 80% by weight or more of krill phospholipids.
 13. (canceled)
 14. The liquid composition of claim 8, wherein the krill phospholipids are a mixture of phospholipid compounds of formula (I) as defined herein: 